EP4487063A1

EP4487063A1 - Method for controlling a hydronic system

Info

Publication number: EP4487063A1
Application number: EP23708709.3A
Authority: EP
Inventors: Jan Plougmann
Original assignee: Grundfos Holdings AS
Current assignee: Grundfos Holdings AS
Priority date: 2022-03-01
Filing date: 2023-02-23
Publication date: 2025-01-08
Also published as: CN118696202A; US20250189144A1; WO2023165900A1

Abstract

The invention to a method for controlling a hydronic system having a thermal source (2) and at least a first (4) and a second (6) load circuit connected to the thermal source via a hydraulic system (8) having a changeover valve (16), said changeover valve (16) being configured to selectively activate a flow of heat transfer medium through the first (4) or the second (6) load circuit, wherein for distributing the required thermal energy to the load circuits (4, 6) in at least one operational condition a duty cycle for the first load (4) circuit is extended, resulting in a shortening of the duty cycle of the second load circuit (6), and for compensating this shortening of the duty cycle the temperature and/or flow of the heat transfer medium supplied to the second load circuit (6) are adjusted, as well as a hydraulic unit for a hydronic system.

Description

Applicant: GRUNDFOS HOLDING A/S

Title: Method for controlling a hydronic system

Our Ref.: GP 3565 WO

Description

[01 ] The invention refers to a method for controlling a hydronic system having at least two load circuits and to a hydraulic unit for such a hydronic system.

[02] Hydronic systems like heating or cooling systems in buildings often comprise several load circuits. In those systems it is a problem to optimally distribute the thermal energy to the different circuits. Furthermore, there may be different load circuits operated with different feet temperatures, like for example floor heating circuits and radiator-circuits. A further problem may be occurring noise, in particular in heating circuits using radiators.

[03] In view of these problems it is the object of the invention to provide a method allowing an optimized energy distribution in a hydronic system having at least two load circuits. This object is achieved by a method having the features defined in claim 1 and by a hydronic unit having the features defined in claim 10. Preferred embodiments are defined in the dependent subclaims, the following description and the accompanying drawings.

[04] The control method according to the invention is provided for controlling a hydronic system, i.e. a hydraulic heating and/or cooling system. Such a hydronic system has a thermal source like a cooling or heating source. A heating source for example may be a boiler, a heat pump or a solar heating system. In a cooling system the thermal source may be a chiller. Those thermal sources may be connected directly or via a heat exchanger. The hydronic system comprises at least a first and a second load circuit, for example load circuits for heating and/or cooling different parts of a building, for example different rooms. In a building those load circuits for example may be floor heating circuits and/or heating circuits comprising radiators. In the hydronic system to be used with the method according to the invention the different load circuits are connected to the thermal source via a hydraulic system having a changeover valve. The changeover valve is configured to selectively activate a flow of heat transfer medium through the different load circuits, i.e. the at least first and second load circuit. This means, the load circuits are not supplied in parallel but selectively, such that during a supply of a first load circuit the second load circuit is not supplied with a heat transfer medium, i.e. a liquid heat transfer medium, and vice versa. The liquid heat transfer medium may for example be water, glycol or any other suitable heat transfer medium.

[05] According to the method, the duty cycles for the load circuits can be adjusted for distributing the required thermal energy. According to the method in at least one operational condition a duty cycle for the first load circuit may be extended. Due to the selective activation of the circuits this results in a shortening of the duty cycle of the second load circuit or duty cycles of further load circuits. According to the invention this shortening of the duty cycle is compensated by adjusting the temperature and/or the flow of the heat transfer medium supplied to the second load circuit, which second load circuit has the shortened duty cycle. This method in particular is advantageous for hydronic systems having different kinds of load circuits, for example one load circuit comprising radiators and another load circuit being a floor heating circuit. These different kinds of load circuits have different properties and requirements which can be used in an optimized way to achieve an optimized energy distribution over all the load circuits with a minimized total energy consumption. For example one load circuit can be supplied with a higher flow and/or temperature to compensate the shortening of its duty cycle, wherein the other load circuit may be supplied with a lower temperature and/or flow but has extended duty cycle instead.

[06] In a preferred embodiment the duty cycle, temperature and/or flow of the heat transfer medium are set on basis of the energy demand of the respective load circuit. This allows to increase comfort and reduces the energy consumption, since oversupply or undersupply of a load circuit can be avoided. Preferably, by the method according to the invention the supply of thermal energy is adjusted such that it substantially corresponds to the energy demand of the respecting load circuit.

[07] Preferably, the energy demand of at least one of the load circuits is detected on basis of a temperature difference between supply and return temperature detected in the respective load circuit and the flow inside the respective load circuit. The temperature difference and the flow define the energy supplied to the load circuit. If the temperature difference is too small, i.e. the return temperature is too high, for example, the energy supply is too high.

[08] According to a further embodiment said pressure and/or flow of the heat transfer medium in the first load circuit are set to avoid noise occurring in this first load circuit, wherein preferably the flow is limited to a maximum flow. Noise, for example, may be a problem in heating circuits having radiators. If the flow is too high there may occur noise, in particular if thermostatic valves of the radiators are partly closed. Therefore, it may be desired to not exceed a maximum flow and/or pressure in the respective load circuit. However, according to the invention this may be compensated by an extended duty cycle ensuring a sufficient energy supply in this first heating circuit. [09] According to a further embodiment the temperature and/or flow of the heat transfer medium supplied to the second load circuit are adjusted if the energy demand cannot be satisfied at a maximum duty cycle for this second load circuit. For example, if the hydronic system is a heating system, the temperature may be increased and/or the flow may be increased to increase the energy supply without extending the duty cycle. In case of a cooling system the temperature may be lowered and/or the flow may be increased to compensate a reduced duty cycle or to ensure a required energy supply at a maximum duty cycle. In case of a cooling system, actually, the energy supply is an energy removal, since heat is removed from the object to be cooled. The second load circuit for example may be a floor heating circuit. In a floor heating circuit a higher flow may be accepted, since occurring noise is a minor problem.

[10] In a system selectively activating the first and the second load circuit or the different load circuits the maximum duty cycle for the second load circuit may be defined by a minimum duty cycle for the first load circuit. When the first load circuit is open, the second load circuit is closed. Thus, the maximum opening time or duty cycle for the second load circuit is limited by the minimum opening time or duty cycle of the first load circuit.

[1 1 ] Preferably, the temperature of the heat transfer medium is adjusted by a mixing valve which mixes a supply flow from the thermal source with a return flow in an adjustable mixing ratio. Such mixing valve allows to adjust the supply temperature independent from the outlet temperature of a thermal source. For example, in a heating system it is possible to reduce the supply temperature compared to the outlet temperature of a boiler. In a cooling system, for example, it is possible to increase the supply temperature compared to the outlet temperature of a chiller. Furthermore, by such a mixing device or mixing valve the supply temperatures for the different load circuits, i.e. at least the first and the second load circuit, can be set differently. For example, a floor heating circuit can be supplied with a lower supply temperature than a heating circuit having radiators. The mixing device or mixing valve allows to adjust the temperature of the heat transfer medium as explained before.

[12] The flow of the heat transfer medium may be adjusted by controlling the speed of a circulator pump in the hydronic system. By increasing the speed the flow can be increased and by decreasing the speed the flow can be decreased. To adjust the speed of the circulator pump the circulator pump preferably has an electronic control having a frequency converter allowing to change the rotational speed of the pump’s drive motor.

[13] Preferably, the changeover valve, the flow of the heat transfer medium and/or the temperature of the heat transfer medium are controlled by a central control device which control device preferably is integrated into a circulator pump unit, preferably in the circulator pump unit providing the flow in the hydronic system, i.e. the flow through the load circuits. The central control allows to easily adjust all the parameters like temperature, flow, pressure and/or duty cycle as explained before. The integration of the control into the circulator pump simplifies the system, since there is only one main control unit in the hydronic system providing all necessary control functions for an optimized heat distribution in the hydronic system.

[14] Beside the method as explained above the invention refers to a hydraulic unit for a hydronic system. Such hydraulic unit preferably is suitable to carry out the method as discussed above. Therefore, preferred embodiments as described with reference to the method should be regarded as preferred solutions for the hydraulic unit, too, and vice versa.

[15] The hydraulic unit for a hydronic system according to the invention comprises a thermal source inlet and a thermal source outlet. These are for example used for connection with a heating source like a boiler or heat pump or a cooling source like a chiller. Furthermore, the unit comprises at least one first load circuit connection and at least one second load circuit connection. These first and second load circuit connections include feed and return connections. It is not required to have both separate feed and return connections for each circuit. For example, there may be a first feed connection for a first load circuit and a second feed connection for a second load circuit and a common return connection. The different load circuits, i.e. the at least one first and the at least one second load circuit are connected to the load circuit connections by a suitable piping. Furthermore, the hydraulic unit comprises a changeover valve which is connected to the first load circuit connection and to the second load circuit connection and configured to selectively activate a flow of heat transfer medium through the first or the second load circuit. This means the changeover valve can switch the flow between the first and the second load circuit. When the flow is directed to the first load circuit there is no flow through the second load circuit and vice versa. Furthermore, the unit comprises a control device for controlling said changeover valve. According to the invention said control device is configured such that for distributing the required thermal energy to the different load circuits, i.e. at least the first and the second load circuit, the changeover valve is controlled to achieve a desired heat distribution to the different load circuits. The control device is configured such that in at least one operational condition a duty cycle for the first load circuit is extended which results in a shortening of the duty cycle of the second load circuit. By this, the thermal energy supplied to the first load circuit is increased. For compensating this shortening of the duty cycle of the second load circuit the control device is configured such that the temperature and/or the flow of the heat transfer medium supplied to the second load circuit are adjusted. This can be achieved by outputting respective control signals to temperature adjusting means and/or flow adjusting means. For example, there may be an output temperature control signal to a thermal source requiring the adjustment of the temperature.

[16] According to a preferred embodiment the hydraulic unit comprises a mixing device acting as a temperature adjusting means. The mixing device is configured to adjust the temperature of a heat transfer medium by admixing a return flow. In a heating system a cold return flow may be admixed to a supply flow to reduce the temperature. In a cooling system a return flow may be admixed to a supply flow to increase the supply temperature. Preferably, said mixing device is controlled by said control device. Thus, the hydraulic unit preferably has an integrated temperature control device.

[17] According to a possible embodiment said mixing device comprises a mixing valve which is driven by an electric, magnetic or thermal electric actuator. These may be controlled by electric control signals output by said control device. The actuator preferably is connected to a moveable valve element adjusting the mixing ratio between two flow paths depending on the position of the valve element.

[18] Furthermore, according to a further preferred embodiment the hydraulic unit comprises a circulator pump producing a flow of heat transfer medium, wherein said circulator pump is controlled by said control device. In particular, the circulator pump may be configured such that the flow can be adjusted, for example by a speed control. The circulator pump may have an electric drive motor with an electronic control, in particular a control having a frequency converter, to adjust the rotational speed of the drive motor. The speed may be set by an electric control signal output by the control device. According to a further possible embodiment, the control device may be integrated into a control device of the circulator pump.

[19] Preferably, said control device is arranged within a motor housing of the circulator pump and/or within an electronics housing attached to the motor housing of the circulator pumps. In such a design preferably all required control electronics for the hydraulic unit and preferably the hydronic system can be integrated into a single device being part of the circulator pump. This simplifies the installation and reduces the numbers of required electronic components.

[20] According to a special embodiment said changeover valve comprises a valve element which is moveable by a flow and/or pressure of the heat transfer medium. Thus, no separate drive for the changeover valve is required. The flow and pressure moving the valve element of the changeover valve may be produced by a circulator pump, preferably the same circulator pump providing the flow through the load circuits. That circulator pump preferably is controlled by said control device such that the flow and/or pressure are adjusted by the control device to change the position of the valve element. The control device may in particular adjust the acceleration of the drive motor to move the valve element into different valve positions. The changeover valve and the related control device may for example be configured as known from EP 3 376 037 Bl . Such a valve does not need a separate valve drive or actuator, but is moved by the energy produced by the circulator pump. Furthermore, the valve can be controlled by the control of the circulator pump. Thus, according to this embodiment by control of the circulator pump the flow and/or pressure can be adjusted and the changeover valve can be moved to selectively direct the flow through one of the load circuits. For adjusting the heat temperature, preferably a mixing valve having a separate actuator as described above is used. However, it would also be possible to use a valve allowing to change the mixing ratio which is activated by the circulator pump.

[21 ] In the following the invention is described by way of example with reference to the accompanying drawings. In these:

Fig. 1 schematically shows a hydronic system comprising a hydraulic unit according to the invention.

Fig. 2 shows a side view of a hydraulic unit used in hydraulic system according to fig. 1 ,

Fig. 3 shows a perspective view of the hydraulic unit according to fig. 2, and

Fig. 4 a flow chart showing an example for the method according to the invention.

[22] Fig. 1 shows an example of a hydronic system in form of a heating system. The system comprises a thermal source, in this example a boiler 2, a first load circuit 4, in this case a radiator heating circuit, and a second load circuit 6, in this example a floor heating circuit. For supplying the first load circuit 4 and the second load circuit 6 with thermal energy delivered by the boiler 2, there is arranged a hydraulic device, i.e. an integrated hydraulic unit 8. The thermal energy is transferred via a heat transfer medium circulating in the hydraulic system and transferred and distributed by the hydraulic unit 8 comprises a circulator pump 10 with a control unit or control device 12. The circulator pump 10 circulates the heat transfer medium in the hydraulic system. The control device 12 is arranged in a motor and electronics housing 14 attached to the circulator pump 10, i. e. to the pump housing of the circulator pump 10. Furthermore, the hydraulic unit 8 comprises a changeover valve 16 and a mixing valve 18. The changeover valve 16 and the mixing valve 18 are controlled by the control device 12, which is provided for control of the circulator pump 10, too. The hydraulic unit 8 comprises six hydraulic connections or ports A-F. A first hydraulic connection A and a second hydraulic connection B are connected with a changeover valve 16 which can selectively connect one of the connections A and B with the inlet or suction side of the circulator pump 10. In this example the first hydraulic connection A is a return for the second load circuit, whereas the hydraulic connection B acts as a return port for the first load circuit 4. The third hydraulic connection or port C is an inlet port connected to the boiler 2, i. e. is a feed connection through which hot heat transfer medium, like water, enters the hydraulic unit 8. The fourth hydraulic connection D is a feed connection connected to the inlet side of the second load circuit 6. The fifth hydraulic connection or port E is a feed connection for the first load circuit 4 and the sixth hydraulic connection F is a return connection connected to a return line towards the boiler 2.

[23] Inside the hydraulic unit 8 there is a flow path 20 directly connecting the two hydraulic connections C and E allowing a direct fluid flow from the outlet side of the boiler 2 towards the feed or inlet side of the first load circuit 4. The mixing valve 18 is connected to the hydraulic connection C, too, and on its outlet side connected to the hydraulic connection D being a feed connection for the second load circuit 6. There is a further flow path 22 connecting the outlet or pressure side of the circulator pump 10 with the third port of the mixing valve 18. Via this flow path 22 heat transfer medium from the return of the load circuits 4, 6 flows towards the mixing valve 18. Inside the mixing valve a flow from the flow path 22 and a flow from the hydraulic connection C are mixed to reduce the temperature of the fluid entering via port C and to provide a reduced temperature of heat transfer medium at the hydraulic connection or port D, i. e. the feed towards the second load circuit 6, which preferably is a floor heating circuit. The mixing ratio achieved by the mixing valve 18 is adjusted by the control device 12 connected to an actor 24, for example a thermoelectric actor moving or adjusting the mixing valve 18. The changeover valve 16 is controlled by the control device 12, too, either by an electric actor integrated into the changeover valve 16 or hydraulically via pressure and/or flow produced by the circulator pump 10. The changeover valve 16 depending on its valve position activates a fluid flow through the first load circuit 4 or the second load circuit 6 by opening the respective return connection.

[24] For the control in this example, there are provided three temperature sensors Ti, T2, and T3. Furthermore, there is a flow detection means or flow sensor S integrated into the circulator pump 10. All the sensors are connected to the control device 12 so that the control device 12 can control the actors and the circulator pump 10 based on values detected by these sensors.

[25] The temperature sensor Ti detects the supply temperature for the first load circuit 4. The temperature sensor T2 detects the supply temperature for the second load circuit 6 and the third temperature sensor T3 detects the return temperature from the load circuit 4 or 6, depending on the switching position of the changeover valve 16. Furthermore, the control device 12 detects the flow provided by the circulator pump 10. This may be done by a separate flow sensor or the flow S can be derived from electrical parameters detected in the pump 10. On basis of the inlet temperature and the outlet temperature and the flow the control device 12 calculates the energy demand, i.e. the actual and current energy demand of the activated load circuit 4 or 6.

[26] The control device 12 is configured to adjust the duty cycle for the two load circuits 4 and 6, i.e. the duration for which the respective load circuit 4, 6 is switched on by use of the changeover valve 16. The inlet temperature of the second load circuit 6 can be adjusted by controlling the mixing valve 18. Furthermore, the control device 12 is configured to adjust the flow S by control of the circulator pump 10. Since the changeover valve 16 is configured such that it selectively switches on the return connection for the two load circuits 4 and 6, i.e. can activate the load circuits 4 and 6 in an alternating manner, the duty cycles of the two load circuits 4 and 6 affect each other.

[27] The control device 12 is configured such that preferably a required amount of thermal energy is transferred to the respective load circuits 4, 6. In case of a heating system as shown in this example heat is transferred to the load circuits 4 and 6 via a liquid heat transfer medium, like for example water. In case of a cooling system heat is transferred from the load circuits 4 and 6 to a cooling device or chiller which would be installed instead of the boiler 2. For simplifying the description of both a cooling and a heating system such cooling is regarded as an input of thermal energy into the respective load circuits, too.

[28] To compensate the dependency or influence of the duty cycles the control device 12 is configured to carry out a compensation method ensuring the required supply of thermal energy for all load circuits. In case that the first load circuit 4 having the radiators require an increase of thermal energy supplied, the duty cycle of this first load circuit may be extended by the control device 12, i.e. the duration in which the return of the first load circuit 4 is connected to the circulator pump 10 via the changeover valve 16 is extended. If the switch on duration or duty cycle is increased for the first load circuit 4 this minimizes the maximum switch on duration or duty cycle of the second load circuit 6, since the entire switch on duration or duty cycle of all load circuits cannot exceed 100%. Thus, during the remaining maximum switch on duration for the second load circuit 6 the load circuit 6 must be supplied with the necessary thermal energy. To compensate the reduced switch on duration or duty cycle the control device 12 enlarges the flow of heat transfer medium supplied by the circulator pump 10 during activation of the second load circuit 6 and/or increases the feed temperature of the heat transfer medium at the hydraulic connection D by respective control or activation of the mixing valve 18.

[29] Since the supply for the first load circuit 4, i.e. the hydraulic connection E is directly connected to the inlet port or hydraulic connection C the feed temperature always corresponds to the feed temperature supplied by the boiler 2. This means for this circuit the supplied thermal energy can not be increased by increasing the temperature, since the feed temperature supplied by the boiler 2 is a maximum available feed temperature. Furthermore, increasing the flow S in a radiator circuit like the load circuit 4 is not favorable, since in particular in radiators a too high flow may result in occurring noise, in particular if thermostat valves of the radiators are not completely open. However, since the second load circuit 6 being a floor heating circuit is operated with the reduced temperature provided by the mixing valve 18, it is possible to increase the feed temperature at the hydraulic connection D supplied to the second load circuit 6 by certain amount without disadvantages. Furthermore, it is also possible to increase the flow, since occurring noise in a floor heating circuit is a minor problem compared to a radiator circuit. Thus, by extending the duty cycle of the first load circuit 4 to increase the supplied thermal energy and increasing flow and/or temperature for the second load circuit 6 instead it is possible to deliver the required amount of thermal energy to all load circuits without decreasing the comfort, for example by occurring noise. This means that by the described control provided by the control device 12 an optimized energy distribution to the load circuits with an optimum comfort can be realized.

[30] Since the energy demand of the load circuits 4 and 6 is evaluated during operation via measuring the temperature difference between temperature sensors Ti and T3 for the first load circuit 4 and the temperature difference between the temperature sensor T2 and the temperature sensor T3 for the second load circuit 6 with consideration of the flow S as detected in the circular pump 10, it is required to periodically switch on the load circuits 4 and 6 by switching the changeover valve 16 into the required switching position. Thus, periodically the energy demand of the respective load circuit can be evaluated and the duty cycle, temperature and the flow are periodically recalculated by the control device 12 to adjust the delivered amount of thermal energy for both load circuits 4 and 6.

[31 ] In the flow chart according to figure 4 the essential steps of the described method are shown. In step SI the energy demand for a first load circuit 4 is detected as described before. Then, in the second step S2 it is evaluated by the control device 12 whether the energy demand of the first load circuit is satisfied by the current settings of the hydraulic unit 8. If the energy demand is satisfied, step SI is repeated for example after a predefined period of time. If the energy demand is not satisfied, in step S3 the duty cycle for the first load circuit 4 is extended. In the following step S4 it is evaluated by the control device 12 whether with a new setting of the duty cycle for the first load circuit 4 the energy demand of a second load circuit 6 can still be satisfied or whether for compensation the temperature and/or flow of the heat transfer medium supplied to the second load circuit 6 should be increased, as explained above. If necessary, flow and/or temperature of the heat transfer medium are increased to compensate the reduced duty cycles resulting from the increase of the duty cycle of the first load circuit 4. Then, in the following step S5 it is evaluated whether the new settings for the second load circuit 6 are sufficient, i.e. whether the energy demand of the second load circuit 6 can be satisfied. If yes, the control procedure is restarted at step SI , for example after a predefined period of time. If the energy demand of the second load circuit 6 is not satisfied by this adjusted setting, step S4 is repeated, and the setting is adjusted by further increasing temperature and/or flow. It has to be understood that this flow chart according to figure 4 shows the essential steps of the method in a simplified manner. In practice, the control procedure may include further steps, in particular evaluation and control steps.

List of reference numerals

2 boiler

4 first load circuit

6 second load circuit 8 hydraulic unit

10 circulator pump

12 control device

14 motor and electronics housing

16 changeover valve 18 mixing valve

20 flow path

22 flow path

24 actor

A-F hydraulic connections Ti, T2, T3 temperature sensors

S flow detection means

Claims

1 . Method for controlling a hydronic system having a thermal source (2) and at least a first (4) and a second (6) load circuit connected to the thermal source via a hydraulic system (8) having a changeover valve (16), said changeover valve (16) being configured to selectively activate a flow of heat transfer medium through the first (4) or the second (6) load circuit, characterized in that for distributing the required thermal energy to the load circuits (4, 6) in at least one operational condition a duty cycle for the first load (4) circuit is extended, resulting in a shortening of the duty cycle of the second load circuit (6), and that for compensating this shortening of the duty cycle the temperature and/or flow of the heat transfer medium supplied to the second load circuit (6) are adjusted.

2. Method according to claim 1 , characterized in that the duty cycle, temperature and/or flow of the heat transfer medium are set on basis of the energy demand of the respective load circuit (4, 6).

3. Method according to claim 1 or 2, characterized in that the energy demand of at least one of the load circuits (4, 6) is detected on basis of a temperature difference between supply and return temperature (Ts) detected in the load circuit (4, 6) and the flow (S) inside the respective load circuit.

4. Method according to one of the preceding claims, characterized in that pressure and/or flow of the heat transfer medium in the first load circuit (4) are set to avoid noise occurring in the first load circuit (4), wherein preferably the flow is limited to a maximum flow. Method according to one of the preceding claims, characterized in that the temperature and/or flow of the heat transfer medium supplied to the second load circuit (6) are adjusted if the energy demand cannot be satisfied at a maximum duty cycle for the second load circuit (6). Method according to one of the preceding claims, characterized in that the maximum duty cycle for the second load circuit (6) is defined by a minimum duty cycle for the first load circuit (4). Method according to one of the preceding claims, characterized in that the temperature of the heat transfer medium is adjusted by a mixing device or mixing valve (18) which mixes a supply flow from the thermal source (2) with a return flow in an adjustable mixing ratio. Method according to one of the preceding claims, characterized in that the flow of heat transfer medium is adjusted by controlling the speed of a circulator pump (10) in the hydraulic system (8). Method according to one of the preceding claims, characterized in that the changeover valve (16), the flow of the heat transfer medium and/or the temperature of the heat transfer medium are controlled by a central control device (12), which control device (12) preferably is integrated into a circulator pump unit (10). 10. Hydraulic unit for a hydronic system, comprising a thermal source inlet (C) and a thermal source outlet (F), at least one first load circuit connection (B) and at least one second load circuit connection (A), a changeover valve (16) connected to the first load circuit connection (B) and to the second load circuit connection (A) and configured to selectively activate a flow of heat transfer medium through the first (4) or the second load circuit (6), and a control device (12) controlling said changeover valve (16), characterized in that said control device (12) is configured such that for distributing the required thermal energy to the load circuits (4, 6) by control of the changeover valve (16) in at least one operational condition a duty cycle for the first load circuit (4) is extended, resulting in a shortening of the duty cycle of the second load circuit (6), and that for compensating this shortening of the duty cycle the temperature and/or flow of the heat transfer medium supplied to the second load circuit (6) are adjusted.

1 1. Hydraulic unit according to claim 10, characterized by a mixing device (18) being configured to adjust the temperature of a heat transfer medium by admixing a return flow, wherein said mixing device (18) is controlled by said control device (12).

12. Hydraulic unit according to claim 10 or 1 1 , characterized in that said mixing device comprises a mixing valve (18) driven by an electric, magnetic, or thermoelectric actor (24).

13. Hydraulic unit according to one of the claims 10 to 12, characterized by a circulator pump (10) producing a flow of heat transfer medium, wherein said circulator pump (10) is controlled by said control device (12). Hydraulic unit according to one of the claims 10 to 13, characterized in that said control device (12) is arranged within a motor housing (14) of the circulator pump (10) and/or within an electronics housing attached to the motor housing (14) of the circulator pump (10). Hydraulic unit according to one of the claims 10 to 14, characterized in that said changeover valve (16) comprises a valve element movable by a flow and/or pressure of the heat transfer medium, the flow and pressure are produced by a circulator pump (10), and that said circulator pump (10) is controlled by said control device (12) such that the flow and/or pressure are adjusted by the control device (12) to change the position of the valve element.